There is a need for electrophotographic image forming apparatuses with high energy efficiency and low running costs. Therefore, the development of apparatuses in which fixing temperature is set to be low is being actively performed.
Low temperature fixable toners for electrostatic image development that are usable for such apparatuses (hereinafter simply referred to also as “toners”) have some practical problems. More specifically, one problem when a low-temperature fixable toner is used for an image forming apparatus for high-speed mass printing is that, if fusion of the toner during fixation advances to the extent that its viscosity decreases significantly, a hot offset phenomenon occurs in which part of the fused toner is transferred to a fixing member, causing image contamination. Another problem is that the post-fixing separability of the toner from the fixing member is reduced and this causes an image supporting material together with the toner to be wound around the fixing member.
To achieve both low-temperature fixability and hot offset resistance simultaneously, studies focused on binder resins making up toners are being performed, and various proposals have been made.
For example, Patent Literature 1 describes that in order to achieve both the low-temperature fixability and the hot offset resistance simultaneously, ethylene glycol dimethacrylate serving as a cross-linking agent together with a binder resin is added to a toner to facilitate a cross-linking reaction.
However, when the cross-linking agent is added to the toner, the resin becomes hard due to the cross-linking effect, so that sufficient low-temperature fixability cannot be obtained with the above toner.
For example, Patent Literature 2 describes that in order to achieve both the post-fixing separability and the hot offset resistance simultaneously without using a releasing agent, a binder resin and polyethylene glycol methacrylate or acrylate (n=12 to 45) are added to a toner.
However, when the above monomer is added to the toner, a significant reduction in glass transition point occurs, and sufficient hot offset resistance cannot be obtained with the above toner. In addition, since no releasing agent is added, sufficient post-fixing separability cannot also be obtained with the above toner.